WebServer Demo Updates

[prodestrian]

Summary

This PR adds additional Webserver demo features, specifically being able to load the HTML page and click "On" and "Off" buttons to toggle the built-in LED state on the ESP8266 (note: Depending on the device model, the built-in LED may be inverted to "On=LOW", ie click "Off" to turn LED on).

Description

• Move Webserver.ino sketch to subfolder (as Arduino IDE requires)
• Move index.html content into data subfolder
• Switch from ESP8266WebServer to ESPAsyncWebServer
• Load HTML content from LittleFS instead of strings
• Add demo code to control the LED_BUILTIN state using HTML button

Arduino IDE Requirements

Install ESPAsyncWebServer

Download and install into Arduino libraries: https://github.com/me-no-dev/ESPAsyncWebServer/archive/master.zip

Install ESPAsyncTCP

Download and install into Arduino libraries: https://github.com/me-no-dev/ESPAsyncTCP/archive/master.zip

Install Arduino ESP8266 LittleFS Filesystem Uploader

Download and install into Arduino Tools: https://github.com/earlephilhower/arduino-esp8266littlefs-plugin (Follow instructions on GitHub README)

[ajquick]

Everything worked for me. Feel free to update with your latest test code though.